Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more fluid filled electric motors coupled to one or more high performance pumps. Each of the components and sub-components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment, which includes wide ranges of temperature, pressure and corrosive well fluids.
Components commonly referred to as “seal sections” protect the electric motors and are typically positioned between the motor and the pump. In this position, the seal section provides several functions, including transmitting torque between the motor and pump, restricting the flow of wellbore fluids into the motor, absorbing axial thrust imparted by the pump, and accommodating the expansion and contraction of the dielectric motor lubricant as the motor moves through thermal cycles during operation and pressure equalization. Many seal sections employ seal bags to accommodate the volumetric changes and movement of fluid in the seal section. Seal bags can also be configured to provide a positive barrier between clean lubricant and contaminated wellbore fluid.
Modern seal sections may include two or more seal bags connected in parallel or series configurations. When seal bags are placed in series, the oil from one bag is kept separate from the oil in another bag by the use of a shaft seal between each section. In this way, seal bags connected in a series configuration function as redundant seals. If the first seal bag is compromised or avoided, the foreign fluid is prevented from going into the motor by the second seal bag.
In contrast, multiple seal bags connected in a parallel configuration do not provide a redundant layer of protection. Instead, seal bags connected in a parallel configuration are intended to simply increase the overall effective volume change capacity within the seal section. In prior art parallel seal bag configurations, there is typically no shaft seal placed between adjacent seal bags and fluid is encouraged to communicate concurrently between bag sections along the shaft. Although effective at increasing fluid exchange capacity, the use of directly connected parallel seal bags presents a concern if a contaminated fluid is allowed to quickly migrate through the parallel seal bags. There is, therefore, a need for an improved seal section that overcomes the deficiencies of the prior art while retaining the benefits of parallel seal bag sections. It is to this and other needs that the present invention is directed.